Elon Musk.Taylor Hill via Getty ImagesElon Musk's OpenAI rival, xAI, says it just raised $6 billion in funding from investors.The AI startup is backed by VCs like Sequoia Capital and Saudi Arabia's Kingdom Holding.Musk said xAI's pre-money valuation was $18 billion.Elon Musk's xAI just took a critical step in building up its war chest to take on Sam Altman's OpenAI.The AI startup said in a blog post on Sunday that it had raised $6 billion for their Series B funding round.The company, which is barely a year old, counts among its investors prominent VCs like Andreessen Horowitz and Sequoia Capital as well as Saudi Arabia's Kingdom Holding."There will be more to announce in the coming weeks," Musk said in an X post on Monday morning.The mercurial billionaire said in a subsequent X post that xAI's pre-money valuation was $18 billion.